#include <gst/gst.h>
 /* Structure to contain all our information, so we can pass it to callbacks */
 typedef struct _CustomData {
   GstElement *pipeline;
   GstElement *source;
   GstElement *convert;
   GstElement *resample;
   GstElement *sink;
 } CustomData;
 /* Handler for the pad-added signal */
 static void pad_added_handler (GstElement *src, GstPad *pad, CustomData *data);
 int main(int argc, char *argv[]) {
   CustomData data;
   GstBus *bus;
   GstMessage *msg;
   GstStateChangeReturn ret;
   gboolean terminate = FALSE;
   /* Initialize GStreamer */
   gst_init (&argc, &argv);
   /* Create the elements */
   data.source = gst_element_factory_make ("uridecodebin", "source");
   data.convert = gst_element_factory_make ("audioconvert", "convert");
   data.resample = gst_element_factory_make ("audioresample", "resample");
   data.sink = gst_element_factory_make ("autoaudiosink", "sink");
   /* Create the empty pipeline */
   data.pipeline = gst_pipeline_new ("test-pipeline");
   if (!data.pipeline || !data.source || !data.convert || !data.resample || !data.sink) {
     g_printerr ("Not all elements could be created.\n");
     return -1;
   }
   /* Build the pipeline. Note that we are NOT linking the source at this
    * point. We will do it later. */
   gst_bin_add_many (GST_BIN (data.pipeline), data.source, data.convert, data.resample, data.sink, NULL);
   if (!gst_element_link_many (data.convert, data.resample, data.sink, NULL)) {
     g_printerr ("Elements could not be linked.\n");
     gst_object_unref (data.pipeline);
     return -1;
   }
   /* Set the URI to play */
   g_object_set (data.source, "uri", "file:///home/cdl/study/gst/test.webm", NULL);
   /* Connect to the pad-added signal */
   g_signal_connect (data.source, "pad-added", G_CALLBACK (pad_added_handler), &data);
   /* Start playing */
   ret = gst_element_set_state (data.pipeline, GST_STATE_PLAYING);
   if (ret == GST_STATE_CHANGE_FAILURE) {
     g_printerr ("Unable to set the pipeline to the playing state.\n");
     gst_object_unref (data.pipeline);
     return -1;
   }
   /* Listen to the bus */
   bus = gst_element_get_bus (data.pipeline);
   do {
     msg = gst_bus_timed_pop_filtered (bus, GST_CLOCK_TIME_NONE,
         GST_MESSAGE_STATE_CHANGED | GST_MESSAGE_ERROR | GST_MESSAGE_EOS);
     /* Parse message */
     if (msg != NULL) {
       GError *err;
       gchar *debug_info;
       switch (GST_MESSAGE_TYPE (msg)) {
         case GST_MESSAGE_ERROR:
           gst_message_parse_error (msg, &err, &debug_info);
           g_printerr ("Error received from element %s: %s\n", GST_OBJECT_NAME (msg->src), err->message);
           g_printerr ("Debugging information: %s\n", debug_info ? debug_info : "none");
           g_clear_error (&err);
           g_free (debug_info);
           terminate = TRUE;
           break;
         case GST_MESSAGE_EOS:
           g_print ("End-Of-Stream reached.\n");
           terminate = TRUE;
           break;
         case GST_MESSAGE_STATE_CHANGED:
           /* We are only interested in state-changed messages from the pipeline */
           if (GST_MESSAGE_SRC (msg) == GST_OBJECT (data.pipeline)) {
             GstState old_state, new_state, pending_state;
             gst_message_parse_state_changed (msg, &old_state, &new_state, &pending_state);
             g_print ("Pipeline state changed from %s to %s:\n",
                 gst_element_state_get_name (old_state), gst_element_state_get_name (new_state));
           }
           break;
         default:
           /* We should not reach here */
           g_printerr ("Unexpected message received.\n");
           break;
       }
       gst_message_unref (msg);
     }
   } while (!terminate);
   /* Free resources */
   gst_object_unref (bus);
   gst_element_set_state (data.pipeline, GST_STATE_NULL);
   gst_object_unref (data.pipeline);
   return 0;
 }
 /* This function will be called by the pad-added signal */
 static void pad_added_handler (GstElement *src, GstPad *new_pad, CustomData *data) {
   GstPad *sink_pad = gst_element_get_static_pad (data->convert, "sink");
   GstPadLinkReturn ret;
   GstCaps *new_pad_caps = NULL;
   GstStructure *new_pad_struct = NULL;
   const gchar *new_pad_type = NULL;
   g_print ("Received new pad '%s' from '%s':\n", GST_PAD_NAME (new_pad), GST_ELEMENT_NAME (src));
   /* If our converter is already linked, we have nothing to do here */
   if (gst_pad_is_linked (sink_pad)) {
     g_print ("We are already linked. Ignoring.\n");
     goto exit;
   }
   /* Check the new pad's type */
   new_pad_caps = gst_pad_get_current_caps (new_pad);
   new_pad_struct = gst_caps_get_structure (new_pad_caps, 0);
   new_pad_type = gst_structure_get_name (new_pad_struct);
   if (!g_str_has_prefix (new_pad_type, "audio/x-raw")) {
     g_print ("It has type '%s' which is not raw audio. Ignoring.\n", new_pad_type);
     goto exit;
   }
   /* Attempt the link */
   ret = gst_pad_link (new_pad, sink_pad);
   if (GST_PAD_LINK_FAILED (ret)) {
     g_print ("Type is '%s' but link failed.\n", new_pad_type);
   } else {
     g_print ("Link succeeded (type '%s').\n", new_pad_type);
   }
 exit:
   /* Unreference the new pad's caps, if we got them */
   if (new_pad_caps != NULL)
     gst_caps_unref (new_pad_caps);
   /* Unreference the sink pad */
   gst_object_unref (sink_pad);
 }
